Thermal reactors are heated by external lamps which pass infra-red radiations into the reactor chamber through heating ports. Quartz windows covering the ports are transparent to the radiations, and peripherally sealed to prevent reactant gas leaks into the ambient environment.
Flat windows provide a uniform space between the wafer and the inside surface of the window for promoting the orderly flow of reactant gas over the window and uniform deposition of the reactant material onto the wafer. Flat windows are therefore desirable, especially when the reactant gas within the chamber is maintained at about the same pressure as the ambient gas outside the chamber.
However, the reactant gas is frequently maintained at a pressure below ambient creating a pressure differential across the quartz window. Dome shaped covers having an outward bow are employed for opposing the inward compressive force of the ambient gas.
Prior reactor vessels have two sets of interchangeable windows. Flat windows for ambient chamber pressure applications, and domed windows for reduced chamber pressure applications. The reactor must be taken out of production and "opened up" in order to change the window. The resulting "down time" can be extensive because of the complexity of the window changing task. First the system must be cooled downed to room temperature and brought up to ambient pressure, and purged with inert gas. The clamping bolts must be removed, the windows exchanged, and the clamping bolts replaced and torqued. The system must then be purged with HCL at high temperature to remove particulate matter, and "baked out" to drive moisture from the susceptor and the quartz.
Individual reactor vessels may be installed as one of a bank of reactors on a common operation platform. In order to change the window on any one of these individual reactor vessels, the entire bank of reactors must be taken out of production.
Anderson et al (pending U.S. application Ser. No. 07/491,416 filed Mar. 9, 1990 by the present assignee) shows a wafer reactor vessel with opposed quartz covers mounted over upper and lower heating ports. Adams et al (U.S. Pat. No. 4,920,918) issued on May 1, 1990 shows an elongated bowed quartz chamber with open ends.